The objectives of this proposal are to continue prospective, Phase III, randomized therapeutic studies of polycythemia vera. By means of the protocols under study, the optimum therapy amongst phlebotomy, radioactive phosphorus and ancillary agents, resulting in the least morbidity and the longest survival will be selected. The natural history of polycythemia vera is being characterized and the modifying effects of myelosuppressive therapy determined. Recently, a randomized study has been introduced which will test the effect of platelet anti-aggregating agents plus phlebotomy vs. 32-P, the best myelosuppressive treatment. It is expected to produce results which will be of major significance in determining the ultimate treatment. Trials of new agents, such as Hydrea, for treatment of polycythemia and its major symptoms are being utilized to test the efficacy of such programs. Cytogenetic changes are being detected by studies of the bone marrow cells and peripheral blood and histopathologic marrow examinations are being performed in a sequential manner. Additional studies utilizing immunologic surface markers and special stains of marrow and peripheral blood may help early definition of transitional states. It is expected that approximately three to four years will be required to answer the questions remaining concerning the optimum treatment of polycythemia vera.